Integrated circuits with combined control and driver functions are often referred to as smart power devices. Smart power devices combine high intelligence with low power dissipation. They typically have power Metal Oxide Semiconductor, MOS, Field Effect Transistors, FETs, in their output stages designed to operate at higher voltages, such as 15-80 volts as opposed to the normal Complementary Metal Oxide Semiconductor, CMOS, logic voltage of typically 5 volts or less, and logic devices incorporated on the same integrated circuit so that both a driver function and a controller function are provided in a single chip. Many applications exist for smart power devices such as Liquid Crystal Display, LCD, displays, electro/mechanical devices, automobile electronic devices, projection TV, and even High Definition, HDTV.
A technique for fabricating high voltage, HV, MOS devices is described in an article entitled "High Voltage Thin Layer Devices (RESURF Devices)," IEDM Proceedings, 1979, pp 238-241. This technique uses a shallow lightly doped region between the drain and channel regions of the device. This shallow lightly doped region is referred to as a drift region because of the low amount of current carriers (carriers being electrons or "holes") that are available due to the low level of impurity doping and the device is known as a Reduced Surface Field, RESURF, device.
RESURF techniques are utilized in manufacturing high voltage N-channel Lateral Double Diffused MOS, HV NMOS, devices and high voltage P-channel LDMOS, HV PMOS devices. However, problems exist in manufacturing smart power devices containing such RESURF HV PMOS devices. Typically, complicated charge pumping high voltage circuitry techniques are used for HV PMOS devices. Typically the on-resistance of the HV PMOS device is relatively high. For example, an HV PMOS device described in an article entitled "A Coplanar CMOS Power Switch," IEEE J. Solid-State Circuits, vol SC-16, pp 212-226, June 1981, uses a lightly doped pinched resistance as the drift region.
It is accordingly an object of the invention to provide a simple method to manufacture smart power devices which contain high voltage PMOS devices that have low on resistance.
Other objects and advantages will be apparent to those of ordinary skill in the art having reference to the following figures and specification.